1. Field of the Invention
The present invention relates to a large scale display device (hereinafter, also refereed to simply as “display device”) used for e.g., a baseball stadium and a race track, in which a plurality of display units constitute a screen or a display portion, and more particularly to a technique for uniformizing color tone on the whole display portion.
2. Description of the Background Art
A large scale display device is constituted of a plurality of arranged display units consisting of a number of display elements (e.g., LEDs (light emitting diodes)) and circuits for driving and controlling the display elements. Such a display device is required to uniformize a display on the whole screen, and therefore a variety of proposals on manufacture have been made in order to equalize chromaticity, luminance and the like of each color among the display units.
For example, there are variations in chromaticity (wavelength) and luminance of the LEDs among the display elements caused through manufacturing process. For this reason, the LEDs are classified into several ranks by chromaticity (wavelength), luminance and the like in the final test process, and then put in the manufacturing process of the display unit. For example, only the LEDs of limited ranks are selected for one display device and separated (dispersed) by colors on the whole display device. Thus, in the background-art large scale display device, the chromaticity of the whole screen is uniformized by controlling the parts in the manufacturing process.
Further, in the background-art large scale display device, a desired color is obtained by converting the chromaticity of all the display units (in other words, the whole screen of the display device) on the basis of a single (the same) parameter.
In the background-art large scale display device, the chromaticity and the like on the whole device are controlled and set in advance as above. Therefore, when some of a plurality of display units constituting the display device need to be changed or another display unit needs to be added after assembly process for enlargement of the display device, some problem arises. Specifically, first, since the LEDs to be used are classified and limited as discussed above, it is difficult to manufacture the display unit of the same chromaticity later. Further, since the chromaticity on the whole display device is controlled on the basis of a single parameter, it is difficult to equalize the chromaticity of the original display unit and that of changed or added one.
As one of possible solutions for this problem is a constitution in which the chromaticity of each display unit is variable. In such a constitution, however, individual display units have to be controlled. Further, whether the target chromaticity (chromaticity range) is proper or not, or whether all the display units can be controlled to the target chromaticity or not is not sure until the control of the whole display device is completed. In other words, when it is found that the target chromaticity is not proper after the control and when a display unit which can not be controlled to the target chromaticity is found on the way of control, it is necessary to change the target chromaticity and control the chromaticity of the display unit again. Thus, in the constitution where the chromaticity of each display unit is merely variable, there is a problem of needing a lot of time to control the whole display device.
Furthermore, the above problem may arise in a constitution where the light emitting portion of the display unit is constituted of a plurality of sub-units each changeable or individually controllable.